固体激光装置能源系统建模及故障分析

能源系统(PCS)为固体激光装置片状放大系统提供匹配的电脉冲泵浦能量,涉及到高压、大电流的充放电过程,在这个过程中可能发生电容器短路、高低压母排短路等灾难性故障。针对上述情况,建立了能源系统及其三种主要故障的数学模型;通过仿真计算分析了氙灯负载非线性特性对系统模型的影响,提出了加入补偿参数的修正模型,并通过实验验证了其有效性;分析了故障情况下关键元件(阻尼电感、调波电感、储能电容)的耐受能力以及保护措施。     

Phase transitions in a ferromagnetic semiconductor. I

An analysis is given of the conditions for ferromagnetic phase transitions in an idealised semiconductor model containing magnetic ions. The system is described by a constant interaction — 2J/N between the magnetic ions (Spin I) and the electrons, by the energy gapΔ between two infinitely narrow bands and by the concentrationc of the magnetic ions. We find a great variety of ferromagnetic behavior. In particular there exists the possibility for the magnetization to disappear with a first or second order transition as the temperature decreases or increases. Some magnetization curves are evaluated numerically.     

Gearbox vibration monitoring using extended Kalman filters and hypothesis tests

The efficiency of many maintenance programs is heavily dependent on the detection accuracy of the condition monitoring system. Condition indicators that are sensitive to environmental or operational variables of no interest will inevitably reflect irrelevant fluctuations and thus mislead the subsequent analysis. In consideration of this phenomenon, a fully automatic and robust vibration monitoring system for gearboxes is proposed in this study. The primary objective here is on how to exclude the effects of variable load conditions. The proposed technique features a number of appealing advantages, which include extended Kalman filter-based time-varying autoregressive modeling, automatic autoregressive model order selection with the aid of a non-paired two-sample Satterthwaite's t′-test, a highly effective and robust condition indicator (the means of one-sample Kolmogorov-Smirnov goodness-of-fit test), and an automatic alert generating mechanism for incipient gear faults with the aid of a Wilcoxon rank-sum test. Two sets of entire lifetime gearbox vibration monitoring data with distinct variable load conditions were used for experimental validation. The proposed condition indicator was compared with other well-known and/or recently proposed condition indicators. The results demonstrate excellent performance of the proposed technique in four aspects: the effectiveness of identifying the optimum model order, a minimum number of false alerts, constant behavior under variable load conditions, and to some extent an early alert for incipient gear faults. Furthermore, the proposed condition indicator can be directly employed by condition-based maintenance programs as a condition covariate for operational maintenance decision analysis. It provides a quantitative and more efficient means for exchanging condition information with maintenance programs in comparison with the widely used non-parametric time-frequency techniques such as wavelets, which rely on visual inspection.     

A note on Fermi lattice systems with bilinear hamiltonians: The XY model once morse

The dynamics of a v-dimensional Fermi lattice system with a bilinear hamiltonian is derived in a very simple and natural way. Moreover the thermodynamics of this linear system is treated by means of the so-called K.M.S.-equilibrium condition. Some words are devoted to ergodicity. As an example these general results are applied to an XY model and finally, for this concrete situation, attention is paid to the effect of boundary conditions on the elementary excitation spectrum in the thermodynamic limit.     

Spin-lattice coupling coefficients of Mn2+ ions in stacking faults of ZnS

The spin-lattice coupling coefficients (SLCC) of Mn²⁺ ions in axial sites PN of cubic ZnS crystals containing stacking faults have been measured by an uniaxial stress method. These coefficients were correctly interpreted in an ionic model by taking into account the Blume-Orbach mechanism adapted to a C_3v symmetry and a relativistic mechanism whose importance has been previously demonstrated. Finally, a comparison between the experimental SLCC's for Mn₂₊ in the cubic sites and two axial sites PN and AS due to stacking faults shows that they are roughly identical as predicted theoretically.     

Computer simulation of Ti3Al intermetallic cleavage fracture

The decohesion energy and the energy of unstable stacking faults for all cracking planes and dislocation slip systems observed experimentally are calculated using the molecular dynamics method with N-particle atomic potentials. A dimensionless parameter characterizing the brittle behavior of the material is calculated for basis, prism, and pyramid faces in terms of the model elaborated by Kelly et al. and extended by Rice and Thompson. Cleavage in Ti₃Al is due to low decohesion energy values, which facilitates cracking, and high energies of unstable stacking faults, which prevents the formation of a plastic zone and stress relaxation at its vertex.     

Folding model potentials from realistic interactions for heavy-ion scattering

The double-folding model, with “realistic” nucleon-nucleon interactions based upon a G-matrix constructed from the Reid potential, is used to calculate the real part of the optical potential for heavy-ion scattering. The resulting potentials are shown to reproduce the observed elastic scattering for a large number of systems with bombarding energies from 5 to 20 MeV per nucleon. Some representative inelastic transitions are also reproduced. Exceptions are the elastic scattering of ⁶Li and ⁹Be for which the folded potentials must be reduced in strength by a factor of about two.The same effective interactions are shown to give a good account of two particular cases of alpha scattering as well as some cases of nucleon-nucleus scattering. Some typical examples of inelastic heavy-ion scattering are also predicted successfully.Some general properties of the folding model are reviewed and its theoretical basis is discussed. An explicit density-dependence is examined for one particular realistic interaction and found not to change the results. Single nucleon exchange is included in an approximate way and its importance is studied.In addition to being a study of the folding model, this work also provides a systematic and comprehensive optical model analysis of heavy-ion elastic scattering in this energy range.     

Strength statistics and the distribution of earthquake interevent times

The Weibull distribution is often used to model the earthquake interevent times distribution (ITD). We propose a link between the earthquake ITD on single faults with the Earth’s crustal shear strength distribution by means of a phenomenological stick–slip model. For single faults or fault systems with homogeneous strength statistics and power-law stress accumulation we obtain the Weibull ITD. We prove that the moduli of the interevent times and crustal shear strength are linearly related, while the time scale is an algebraic function of the scale of crustal shear strength. We also show that logarithmic stress accumulation leads to the log-Weibull ITD. We investigate deviations of the ITD tails from the Weibull model due to sampling bias, magnitude cutoff thresholds, and non-homogeneous strength parameters. Assuming the Gutenberg–Richter law and independence of the Weibull modulus on the magnitude threshold, we deduce that the interevent time scale drops exponentially with the magnitude threshold. We demonstrate that a microearthquake sequence from the island of Crete and a seismic sequence from Southern California conform reasonably well to the Weibull model.     

A cell model for liquids. II. Exact solution for the restricted cell model for hard,parallel squares

A restricted cell model for hard, parallel squares is presented both in a discrete and a continuous version. The model is solved exactly by means of a transfer matrix method and the thermodynamic properties are calculated. Some correlation functions are also obtained, which show that the long range order decays at least as fast as 1/r ².     

The first estimations of soil-radon activity near faults in Central Mongolia

Estimation of soil-radon activity, Q was first carried out for faults in Central Mongolia. Eight study sites were located in epicentral zones of Mogod (M = 7.8; 05 January 1967) and Avdar (M = 3.8; 22 March 2009) earthquakes, and in the vicinity of Ulaanbaatar, where small seismic events (M = 1.0–2.5) occurred in the past few years. Profile radon surveys were conducted at fifteen faults that differ in size and geodynamic activity, yet clearly topographically manifested as scarps or straightened segments of valleys of ephemeral streams.By applying the formalized method of processing of the survey results, it was possible to reveal radon anomalies and to establish that their shape, intensity and contrast are mainly determined by the structure of the fault zone. Due to heterogeneous permeability of fault zones, shapes and quantitative parameters of radon anomalies are variable at different faults and in individual cross-sections of one and the same fracture. Radon anomalies in Central Mongolia are diverse, yet the most frequent are the cases where (1) a radon anomaly is discontinuous in shape due to the presence of small domains with minimum values of Q; (2) a major part of the anomaly is located in one fault wall; and (3) a fault scarp is marked by a minimum value of Q. In Central Mongolia, intensities of radon anomalies, Q_max near neotectonic faults differ by more than an order of magnitude. The most intense anomaly (20,200 Bq/m³) is registered at Hustai fault in the vicinity of Ulaanbaatar, which indicates the importance of assessment of radon hazard for the capital city of Mongolia, where almost half the population of the country reside. The contrast of radon anomaly, K_Q is determined as a ratio of a maximum value of Q_max to a minimum value of Q_min outside the fault zone; it varies from 1.4 to 17.3 for faults of Central Mongolia. Faults characterized by ultra-high (K_Q > 10), high (10 ≥ K_Q > 5), increased (5 ≥ K_Q > 3), medium (3 ≥ K_Q > 2) and low (K_Q ≤ 2) radon activity are distinguished. A relative index, K_Q can be effectively applied for assessment of geodynamic activity of faults in Central Mongolia. On the one hand, it correlates with sizes and seismic potential of the studied faults; on the other hand, it significantly reduces the complicating influence of regional factors, such as radioactivity of rocks, sediment thickness, meteorological conditions of measurements, etc.The application of K_Q, the formalized method of detection of radon anomalies, long-distance base cross-sections, and reduction of the measurement interval near faults – these key features of the profile survey are recommendable for further more accurate estimations on the basis of the first measurements of soil-radon activity in Central Mongolia.     

Generalizing the O(N)-field theory to N-colored manifolds of arbitrary internal dimension D

We introduce a geometric generalization of the O(N)-field theory that describes N-colored membranes with arbitrary dimension D. As the O(N)-model reduces in the limit N → 0 to self-avoiding polymers, the N-colored manifold model leads to self-avoiding tethered membranes. In the other limit, for inner dimension D → 1, the manifold model reduces to the O(N)-field theory. We analyze the scaling properties of the model at criticality by a one-loop perturbative renormalization group analysis around an upper critical line. The freedom to optimize with respect to the expansion point on this line allows us to obtain the exponent ν of standard field theory to much better precision that the usual 1-loop calculations. Some other field theoretical techniques, such as the large N limit and Hartree approximation, can also be applied to this model. By comparison of low- and high-temperature expansions, we arrive at a conjecture for the nature of droplets dominating the 3d Ising model at criticality, which is satisfied by our numerical results. We can also construct an appropriate generalization that describes cubic anisotropy, by adding an interaction between manifolds of the same color. The two parameter space includes a variety of new phases and fixed points, some with Ising criticality, enabling us to extract a remarkably precise value of 0.6315 for the exponent ν in d = 3. A particular limit of the model with cubic anisotropy corresponds to the random bond Ising problem; unlike the field theory formulation, we find a fixed point describing this system at 1-loop order.     

Parametric study of a (3–76 cm−1) CH3F tunable FIR Raman laser pumped by a line-narrowed (<0.5 GHz) high pressure continuously tunable laser

By pumping with a line-narrowed continuously tunable CO₂ laser, we produced about 70 FIR emissions in CH₃F with an efficiency larger than previous works. Some low J and high J transitions were pumped for the first time. The large number of emissions produced in a single laser system allowed us to verify some scaling laws in energy, pressure and FIR tuning. The results agreed with a simple theoretical model also reported. The scaling model also allowed to compare our results with the other ones reported in previous works.     

One-Way Markov Process Approach to Repeat Times of Large Earthquakes in Faults

One of the uses of Markov Chains is the simulation of the seismic cycle in a fault, i.e. as a renewal model for the repetition of its characteristic earthquakes. This representation is consistent with Reid??s elastic rebound theory. We propose a general one-way Markovian model in which the waiting time distribution, its first moments, coefficient of variation, and functions of error and alarm (related to the predictability of the model) can be obtained analytically. The fact that in any one-way Markov cycle the coefficient of variation of the corresponding distribution of cycle lengths is always lower than one concurs with observations of large earthquakes in seismic faults. The waiting time distribution of one of the limits of this model is the negative binomial distribution; as an application, we use it to fit the Parkfield earthquake series in the San Andreas fault, California.     

Magnetic excitations in ferromagnetic semiconductors,and their study by light scattering

The magnetic excitation spectrum of degenerate ferromagnetic semiconductors, described by the s-f interaction model, is investigated by calculating various Green functions which provide the dynamic response of the system. In addition to the usual acoustic spin-wave mode, there are also an optical spin-wave branch and the Stoner-like continuum of excitations. Some estimates are made for the first order light scattering from ferrmagnetic semiconductors at low temperatures T?T_c.     

On the many-body Van der Waals binding energy of a dense fluid

We consider a dense system of neutral atoms. When the atoms are represented by isotropic oscillators (Drude-Lorentz model) interacting with nonretarded dipole-dipole forces, the binding energy of the system is given exactly by a well-known expression which is written as a sum of two-bond, three-bond, etc., Van der Waals interactions. For a Bravais lattice this expression for the binding energy can be computed numerically to arbitrary accuracy. This has been done for the f.c.c. lattices of the noble-gas solids by Lucas. For a fluid an exact evaluation would require the knowledge of higher-order molecular distribution functions. Various approximations are discussed for this case, the simplest of which is the so-called long-wavelength approximation due to Doniach. When this approximation is checked by comparison with the exact result for a lattice, it turns out that the two-bond contribution leads to a value which is more than twice too large. Some more refined approximations are considered which treat the two-bond contribution exactly. It is pointed out that the model is consistent only if the distance of closest approach between the atoms is not too small.     

Remarques sur la structure électronique des métaux et alliages

We study the validity of the perturbation expansion in the calculation of the effect of a small, periodic potentialV on an electron gas. We show that for two and three dimensions, the total energy of the system up to second order inV, as well as the total electronic density up to first order, is correctly given by such an expansion. On the other hand, this method can lead to uncorrect and diverging results as far as the electronic density per unit energy and all the abovementioned quantities in a one dimensional model are concerned. Some consequences and applications of these results are then briefly reviewed.     

Effects of Cooper pair tunneling on the electronic structure of trilayer cuprate superconductors

Recent angle-resolved photoemission spectroscopy (ARPES) experiment on the optimally doped trilayer cuprate superconductors Bi2223 has revealed a layer variation of both doping density and d-wave gap. In particular, the two outer layers are overdoped with a gap which is larger than the gap for optimally doped single layer cuprates while the inner layer is underdoped with an even larger gap. Here we propose a minimal model composed of three layer t-J Hamiltonian, single particle interlayer tunneling as well as Cooper pair tunneling terms. By using renormalized mean field method, we study the superconducting order parameters and their dependence of tunneling parameters. Some relevant physical quantities have been calculated. Both tunneling effects influence the electronic structure of the trilayer system and their cooperative action may qualitatively explain the ARPES results.     

Boundary crisis and transient in a dissipative relativistic standard map

Some dynamical properties for a problem concerning the acceleration of particles in a wave packet are studied. The model is described in terms of a two-dimensional nonlinear map obtained from a Hamiltonian which describes the motion of a relativistic standard map. The phase space is mixed in the sense that there are regular and chaotic regions coexisting. When dissipation is introduced, the property of area preservation is broken and attractors emerge. We have shown that a tiny increase of the dissipation causes a change in the phase space. A chaotic attractor as well as its basin of attraction are destroyed thereby leading the system to experience a boundary crisis. We have characterized such a boundary crisis via a collision of the chaotic attractor with the stable manifold of a saddle fixed point. Once the chaotic attractor is destroyed, a chaotic transient described by a power law with exponent −1 is observed.     

Phase diagram analysis using a partially associated solution model for III–V binary systems

Some of the physical and thermodynamic properties of III–V liquids can be explained by assuming that the liquids have a dual structure. The thermodynamic model which has been established for the present paper is a partially associated solution model. It was constructed on the assumption of the existence of associated complexes. The asymmetry of the liquidus curve and the amount of excess free energy determined from the phase diagram analysis can be explained by using the model. Some of the thermodynamic parameters obtained in this study are found to have important physical meanings. The interaction parameter between monoatomic species, ω_A,B is in a good agreement with the theoretical value proposed by Stringfellow. The heat of formation of associated complexes can be represented explicitly in terms of the spectroscopic ionicity and the dehybridization factor. The free energy of formation is empirically evaluated to be 20-6(f_i ?0.17)RT?35,000f_iDcal/mol for III–V binary liquids.     

Decomposition of Ising spin of spin-S Ising model

We propose a general method by which an Ising spin of a spin-S Ising model is decomposed into Ising spins less than S. Some exactly solvable spin-S Ising models with S greater than 1/2 are obtained without using Horiguchi's condition or its extended conditions. These systems are reduced to the Ising model of spin ± 1 or an Ashkin-Teller model.